The present invention relates to a method of and to an apparatus for classifying sheets according to the positions of indicia which are provided on the sheets, particularly for classifying paper sheets in dependency on the positions of watermarks and/or other types of impressed and/or imprinted indicia relative to one or more selected edges of the sheets.
It is well known to provide better-quality paper sheets with watermarks. Such indicia should be located at a fixed distance from the tops and/or bottoms and/or lateral edges of the respective sheets. Watermarks are provided in the sheets before a larger panel of coherent sheets is subdivided into sheets of unit length and width. It is desirable to ensure that each watermark occupy a predetermined position relative to the edges of the respective sheet and, therefore, those sheets whose watermarks are improperly positioned are segregated from other sheets when the positions of watermarks deviate from a preselected range of acceptable positions, i.e., when the watermarks are located outside of selected portions of the respective sheets.
In accordance with a presently known proposal, a roll of paper is first subdivided into large panels each of which contains several sheets, and such large panels are subdivided into sheets of unit length in a guillotine type cutter. Orientation of the panels is effected by hand so as to ensure that the watermarks are located at desired distances from the edges. Such operation is cumbersome, slow and unreliable.
Another known proposal involves scanning individual sheets and discarding those wherein the watermarks are outside of an acceptable field.